1. Field of the Invention
The present invention is directed to an analog-to-digital converter circuit for digitization of a high-frequency signal in the megahertz range with large dynamics.
2. Description of the Prior Art
U.S. Pat. No. 5,546,081 discloses an analog-to-digital converter circuit for digitizing an amplitude-modulated analog high-frequency signal. For example, the analog-to-digital converter can be utilized in the high-frequency receiver of a diagnostic magnetic resonance apparatus. The analog-to-digital converter circuit has a controllable amplifier that precedes the actual analog-to-digital converter. The output of the analog-to-digital converter is connected to a divider that in turn reduces the digitized signal according to the preceding amplification. Control signals for the amplifier and the divider are determined by a level recognition element. The gain is set on the basis of the recognized level so that the analog-to-digital converter operates with maximum modulation. A disadvantage of this known circuit is that it can satisfy high demands on the linearity of the analog-to-digital conversion only if the amplifier has a constant gain factor that can be exactly set, and a correspondingly linear analog-to-digital converters must be employed. It is thereby a serious problem to operate this circuit for converting signals which require that the modification of the gain ensue rapidly within a sampling time interval.